Which of the following statement is TRUE about iron response element?
**Core Concept**
The iron response element (IRE) is a specific nucleotide sequence found in the 5' untranslated region (5' UTR) of certain mRNAs. It plays a crucial role in regulating the expression of genes involved in iron metabolism, particularly those encoding proteins responsible for iron storage and transport.
**Why the Correct Answer is Right**
The IRE is a stem-loop structure composed of a conserved sequence of nucleotides. It is recognized by the iron-regulated protein IRE-BP (iron-regulatory protein-binding protein), also known as IRP-1. When iron levels are low, IRE-BP binds to the IRE, preventing the translation of mRNAs that encode proteins involved in iron uptake and storage, such as ferritin. Conversely, when iron levels are high, IRE-BP is unavailable, allowing the translation of these mRNAs to proceed. This regulatory mechanism helps maintain iron homeostasis in the body.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the IRE is not a promoter or enhancer element, but rather a specific regulatory sequence that interacts with IRE-BP.
**Option B:** This option is incorrect because the IRE is not a response element for any other metal ion, but rather a specific iron-regulatory sequence.
**Option C:** This option is incorrect because the IRE is not a structural element of the ribosome, but rather a regulatory sequence found in specific mRNAs.
**Clinical Pearl / High-Yield Fact**
The iron response element plays a critical role in regulating iron metabolism, and dysregulation of this pathway has been implicated in various iron-related disorders, including iron overload and anemia of chronic disease.
**Correct Answer: C. The iron response element is a stem-loop structure in the 5' untranslated region of certain mRNAs that is recognized by iron-regulated protein IRE-BP.**